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For the first question: I think a big part is that other detectors came online, providing much more confidence that LIGO measurements were real gravitational wa

For the first question: I think a big part is that other detectors came online, providing much more confidence that LIGO measurements were real gravitational waves. For the second question: they can infer the masses of the objects in question from the gravitational waves. Generally if the mass is < 2.5 solar masses it has to be a neutron star, and if it’s > 5 it must be a black hole. Keep in mind this isn’t rigorous! The theoretical maximum for neutron stars is a little less than 3 solar masses, and the estimated minimum for a stellar black hole is much more empirical - I think the smallest known is about 3.5. There’s a lot of interesting physics between 2.5 and 5 solar masses - perhaps this is how we’ll discover “quark stars.” I believe our detectors are not sensitive enough to detect the acceleration of normal stars in any physically plausible scenario - I think they would have to be accelerating way too fast to generate waves that are indistinguishable from noise.

AtlasBarfed 6y ago
Could a gravity whip of a large star around the a galactic central black hole make a big enough ripple?
- ojnabieoot 6y ago
  I am not sure and am only a layperson on this (math grad school, physics undergrad) - conceptually you could think of a blue giant orbiting at 0.99c, but a) the orbit would be so large that the actual acceleration is fairly small, or b) the centripetal forces of a small, relativistic orbit would rip the star into pieces. In particular this would dramatically reduce the effective density of the accelerating mass. Having enough gravitational force to retain coherent structure while accelerating quickly enough to generate gravitational waves seems like a tough circle to square.
- simonh 6y ago
  The material in stars is too spread out over a large volume, and stars move too slowly for these systems to detect them. Black hole collisions events last on the order of about 10 milliseconds and emit up to about 40% of their combined mass in gravitational energy. Nothing a star can do is fast or energetic enough to register at those scales.

AtlasBarfed 6y ago

Could a gravity whip of a large star around the a galactic central black hole make a big enough ripple?

ojnabieoot 6y ago
I am not sure and am only a layperson on this (math grad school, physics undergrad) - conceptually you could think of a blue giant orbiting at 0.99c, but a) the orbit would be so large that the actual acceleration is fairly small, or b) the centripetal forces of a small, relativistic orbit would rip the star into pieces. In particular this would dramatically reduce the effective density of the accelerating mass. Having enough gravitational force to retain coherent structure while accelerating quickly enough to generate gravitational waves seems like a tough circle to square.
simonh 6y ago
The material in stars is too spread out over a large volume, and stars move too slowly for these systems to detect them. Black hole collisions events last on the order of about 10 milliseconds and emit up to about 40% of their combined mass in gravitational energy. Nothing a star can do is fast or energetic enough to register at those scales.